The invention relates to electrical cable comprising two or more insulated conductors, preferably copper, and a bare ground conductor, preferably copper, surrounded by a non-metallic sheath (“NM jacket”). Such electrical cable is widely used in the United States building and construction industry, pursuant to Underwriter's Laboratories Standard 719. FIGS. 1 and 2 show exemplary constructions of such cable. Underwriters Laboratories uses an “NM-B” designation for building wire, where “NM” indicates a non-metallic sheath.
Non-metallic sheathed cable is preferred for residential applications such as single-family homes and apartments. It is used both in new construction and remodeling applications. The cable is often pulled through orifices that have been drilled into studs. In many instances, the orifices are not aligned with one another. In remodeling applications where drywall is already in place, the cable may also be pulled around or under studs. The cable has an NM jacket that protects the insulated current-carrying conductors. The NM jacket must remain intact during the pulling process and also strip off easily during installation. Non-metallic sheathed cable is installed by professional electricians as well as do-it-yourself people who are making changes or additions to their home.
A need exists for an NM jacket that is easy to work with. In particular, it has been recognized that an NM jacket with improved slip characteristics is needed that allows one or more electrical conductors enveloped by an NM jacket to be pulled through unaligned orifices or around studs with less pull force than was required by prior art NM jackets. A need also exists for an NM jacket that is easy to strip. In round NM jacket constructions like the one illustrated in FIG. 2, certain prior art NM jackets are difficult to strip, resulting in damage and lost productivity at the worksite.
A need also exists for a reduced toxicity and environmentally-friendly NM jacket. NM jackets are handled directly by consumers. The use of materials like lead (Pb) can cause health and environmental concerns. Thus, such materials should be avoided in a chemical formulation for an NM jacket. An NM jacket should be lead-free and should minimize or eliminate the incorporation of known and suspected carcinogens and known and suspected environmental hazards. Additionally, it was recognized that a chemical formulation for a lead-free NM jacket should be easy to process during extrusion.